Please, cite this online document as:
Sykora S., Perspectives of Passive and Active Magnetic Resonance in Astronomy,
22nd Valtice NMR, Valtice (Czech Republic), 15-18 Apr 2007, DOI: 10.3247/SL2Nmr07.005.

Abstract

At the 2006 National Congress of GIDRM (the Italian NMR Discussion Group) I have presented a talk [1] aimed at establishing magnetic resonance astronomy (MRA) as a new branch of magnetic resonance (MR). It started with these words:

"The Universe harbors many magnetic bodies, ranging from planets and stars (fractions of a Tesla) to dwarf stars (intermediate fields), pulsars (10^8 T) and magnetars (10^11 T). Since the Universe is made mostly of spinning particles endowed with magnetic moments ..., it is evident that magnetic resonance (MR) phenomena should be commonplace. Yet practical astronomy so far does not seam to take into account the possibility of detecting such phenomena, nor does it strive to exploit them actively on planetary and solar-system scales."

It went on pointing out specific features which might enable us to distinguish radiation emissions due to the presence of magnetic particles (spin radiation). The discussion brought forward and stressed the known fact [2] that we presently do not have any coherent and universal description of magnetic resonance phenomena. Instead, we use in a complementary way two completely different approaches:
> To detect signals, we use just classical induction laws. Since no radiation enters/exits the coil, quantum description would require quantum electrodynamics and the exchange of virtual photons but, so far, no theoretician ever tried to carry it through.
> To explain why NMR and ESR resonance lines are so sharp, we can't avoid quantum physics. We say that there are sharp energy levels and therefore photons get absorbed and emitted at very specific frequencies. But no experimentalist ever actually carried out an MR experiment involving remote excitation and detection

After a brief overview of the goals of MRA, this presentation tackles the above gap in our understanding of MR phenomena, showing that spin radiation is likely to possess two specific properties of utmost importance for the discipline of MRA:
> Perfect chirality (circular polarization) and
> Extreme directionality (alignment along the magnetic field)

While the theoretical reasons for these properties are quite convincing (though not void of shadow areas), an experimental proof of their actual existence is yet to be given and requires means which are beyond the reach of the Author.

The talk concludes with an example of active MRA set-up employing gated, directional and chiral RF transmitter (GDCTx) and receiver (GDCRx) mounted on two space-crafts. Using suitable pulse sequences, the arrangement could be used to carry out localized MR spectroscopy and relaxometry of the atmospheres of magnetic solar-system bodies such as Earth, Jovian planets, and the Sun itself.

References:

[1] Talk: Magnetic Resonance in Astronomy: Feasibility Considerations,
      36th National Congress of GIDRM, Salerno, Italy, September 20-23, 2006.
[2] Hoult D.I., Bhakar B., NMR Signal Reception: Virtual Photons and Coherent Spontaneous Emission,
      Concepts Magn.Resonance, 9, 277-297 (1997)..
[3] D.I.Hoult, N.S.Ginsberg, The Quantum Origins of the Free Induction Decay Signal and Spin Noise,
      J.Magn.Reson. 148, 182 (2001).

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